UI: Only scale HiDPI on QT 5.6+

UI/obs-app.cpp

@@ -29,6 +29,7 @@
 #include <obs-config.h>
 #include <obs.hpp>
 
+#include <QtGlobal>
 #include <QGuiApplication>
 #include <QProxyStyle>
 #include <QScreen>
@@ -1311,7 +1312,9 @@ static int run_program(fstream &logFile, int argc, char *argv[])
 
 	QCoreApplication::addLibraryPath(".");
 
+#if (QT_VERSION >= QT_VERSION_CHECK(5, 6, 0))
 	QApplication::setAttribute(Qt::AA_EnableHighDpiScaling);
+#endif
 
 	OBSApp program(argc, argv, profilerNameStore.get());
 	try {